2,049 research outputs found
Idler-resonant femtosecond optical parametric oscillator with high mid-infra-red beam quality
We report an idler-resonant femtosecond optical parametric oscillator (OPO) with average output power of 520 mW, repetition-rate of 80 MHz, pulse duration of 90 fs and nearly diffraction-limited beam quality at ~2.4 µm
16-µJ pulse energy, picosecond, narrow-linewidth master oscillator power amplifier using direct amplification
We present a gain-switched-diode-seeded 1034.5nm master oscillator power amplifier, employing direct amplification through standard commercial Yb3+-doped fibres to generate 15.6µJ-pulse-energy, 126kW-peak-power, picosecond pulses with 3dB spectral bandwidth of 0.87nm
Model-based object recognition from a complex binary imagery using genetic algorithm
This paper describes a technique for model-based object recognition in a noisy and cluttered environment, by extending the work presented in an earlier study by the authors. In order to accurately model small irregularly shaped objects, the model and the image are represented by their binary edge maps, rather then approximating them with straight line segments. The problem is then formulated as that of finding the best describing match between a hypothesized object and the image. A special form of template matching is used to deal with the noisy environment, where the templates are generated on-line by a Genetic Algorithm. For experiments, two complex test images have been considered and the results when compared with standard techniques indicate the scope for further research in this direction
Hopping Conduction in Disordered Carbon Nanotubes
We report electrical transport measurements on individual disordered carbon
nanotubes, grown catalytically in a nanoporous anodic aluminum oxide template.
In both as-grown and annealed types of nanotubes, the low-field conductance
shows as exp[-(T_{0}/T)^{1/2}] dependence on temperature T, suggesting that
hopping conduction is the dominant transport mechanism, albeit with different
disorder-related coefficients T_{0}. The field dependence of low-temperature
conductance behaves an exp[-(xi_{0}/xi)^{1/2}] with high electric field xi at
sufficiently low T. Finally, both annealed and unannealed nanotubes exhibit
weak positive magnetoresistance at low T = 1.7 K. Comparison with theory
indicates that our data are best explained by Coulomb-gap variable range
hopping conduction and permits the extraction of disorder-dependent
localization length and dielectric constant.Comment: 10 pages, 5 figure
Landau Transport equations in slave-boson mean-field theory of t-J model
In this paper we generalize slave-boson mean-field theory for model to
the time-dependent regime, and derive transport equations for model, both
in the normal and superconducting states. By eliminating the boson and
constraint fields exactly in the equations of motion we obtain a set of
transport equations for fermions which have the same form as Landau transport
equations for normal Fermi liquid and Fermi liquid superconductor, respectively
with all Landau parameters explicity given. Our theory can be viewed as a
refined version of U(1) Gauge theory where all lattice effects are retained and
strong correlation effects are reflected as strong Fermi-liquid interactions in
the transport equation. Some experimental consequences are discussed.Comment: 19 page
Effect of Sun and Planet-Bound Dark Matter on Planet and Satellite Dynamics in the Solar System
We apply our recent results on orbital dynamics around a mass-varying central
body to the phenomenon of accretion of Dark Matter-assumed not
self-annihilating-on the Sun and the major bodies of the solar system due to
its motion throughout the Milky Way halo. We inspect its consequences on the
orbits of the planets and their satellites over timescales of the order of the
age of the solar system. It turns out that a solar Dark Matter accretion rate
of \approx 10^-12 yr^-1, inferred from the upper limit \Delta M/M= 0.02-0.05 on
the Sun's Dark Matter content, assumed somehow accumulated during last 4.5 Gyr,
would have displaced the planets faraway by about 10^-2-10^1 au 4.5 Gyr ago.
Another consequence is that the semimajor axis of the Earth's orbit,
approximately equal to the Astronomical Unit, would undergo a secular increase
of 0.02-0.05 m yr^-1, in agreement with the latest observational determinations
of the Astronomical Unit secular increase of 0.07 +/- 0.02 m yr^-1 and 0.05 m
yr^-1. By assuming that the Sun will continue to accrete Dark Matter in the
next billions year at the same rate as in the past, the orbits of its planets
will shrink by about 10^-1-10^1 au (\approx 0.2-0.5 au for the Earth), with
consequences for their fate, especially of the inner planets. On the other
hand, lunar and planetary ephemerides set upper bounds on the secular variation
of the Sun's gravitational parameter GM which are one one order of magnitude
smaller than 10^-12 yr^-1. Dark Matter accretion on planets has, instead, less
relevant consequences for their satellites. Indeed, 4.5 Gyr ago their orbits
would have been just 10^-2-10^1 km wider than now. (Abridged)Comment: LaTex2e, 17 pages, no figures, 7 tables, 61 references. Small problem
with a reference fixed. To appear in Journal of Cosmology and Astroparticle
Physics (JCAP
Quantum vortex fluctuations in cuprate superconductors
We study the effects of quantum vortex fluctuations in two-dimensional
superconductors using a dual theory of vortices, and investigate the relevance
to underdoped cuprates where the superconductor-insulator transition (SIT) is
possibly driven by quantum vortex proliferation. We find that a broad enough
phase fluctuation regime may exist for experimental observation of the quantum
vortex fluctuations near SIT in underdoped cuprates. We propose that this
scenario can be tested via pair-tunneling experiments which measure the
characteristic resonances in the zero-temperature pair-field susceptibility in
the vortex-proliferated insulating phase.Comment: RevTex 5 pages, 2 eps figures; expanded; to appear in Phys. Rev.
Magnetic excitations in coupled Haldane spin chains near the quantum critical point
Two quasi-1-dimensional S=1 quantum antiferromagnetic materials, PbNi2V2O8
and SrNi2V2O8, are studied by inelastic neutron scattering on powder samples.
While magnetic interactions in the two systems are found to be very similar,
subtle differences in inter-chain interaction strengths and magnetic anisotropy
are detected. The latter are shown to be responsible for qualitatively
different ground state properties: magnetic long-range order in SrNi2V2O8 and
disordered ``spin liquid'' Haldane-gap state in PbNi2V2O8.Comment: 15 figures, Figs. 5,9, and 10 in color. Some figures in JPEG format.
Complete PostScript and PDF available from
http://papillon.phy.bnl.gov/publicat.ht
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